This invention relates to lighting systems. More particularly, the present invention relates to a light emitting diode lighting system which operates in a reduced temperature environment, such as in a refrigerator or freezer unit.
In the grocery store, frozen foods such as juices, ice cream and vegetables, as well as those which need to be maintained at lowered temperatures such as diary products and fresh meat, must be stored in refrigeration units. The refrigeration units which contain these products must be properly lit as the associated shelving and doors create shadows or otherwise block outside ambient light from entering the refrigeration unit.
Flourescent lights have been used in such applications because the flourescent tubes are brighter and generate less heat than incandescent bulbs. However, use of flourescent lights has many drawbacks. Flourescent lights have filaments at each end which output a frequency and generate heat when an appropriate amount of current and voltage applied. The heated filaments warm a mixture of xenon, argon and krypton gas within the flourescent tube causing it to fire and generate light. It is difficult to fire and continue to keep flourescent tubes lit in low temperature environment applications as the mixture of gas must reach and maintain a certain elevated temperature to fire and remain lit. The cold environment acts to lower the temperature of the gas mixture within the flourescent bulb. In fact, flourescent tubes cannot be started in sub-zero temperatures and are very inefficient in colder temperatures above zero. Higher frequencies have been applied to the flourescent tubes to cause the gas mixture to continually generate light, however the high frequency causes electromagnetic interference (EMI) which is costly to filter. Unfiltered EMI caused by the generated high frequencies can cause nearby electronic devices to malfunction or even fail. The flourescent tube filaments are easily broken by vibration and from extreme variations from hot to cold, resulting in a shorter operational life span of the flourescent tubes. In order to partially resolve the problem of operating flourescent bulbs in a cold environment, a surrounding lense and insulator has been disposed around the flourescent tubes' filaments to at least partially retain the heat generated by the flourescent tube filaments.
Flourescent tubes present additional problems when used in cold environment applications. The filaments of the flourescent tubes are easily burnt or broken, and the thin-walled glass used in the flourescent tubes is susceptible to breakage. Flourescent tubes have rated operational lives of only 1,500 to 5,000 hours. Thus, the tubes must frequently be replaced. In fact, it is customary for retailers such as grocery stores to have maintenance contracts wherein all of the flourescent tubes in the refrigeration units are replaced on a schedule well before the rated operational lives of the flourescent tubes so that the service company is not constantly called to replace individual flourescent tubes which have burnt out. Such maintenance increases the cost of operating the refrigeration units.
Ballasts are used in flourescent lighting systems to convert the supplied alternating current to the desired frequency. These ballasts are usually quite large and in their smallest form are fitted into the mullion, or dividing frame, of the refrigeration unit's doors. As either 110V to 240V of alternating current is used to power the flourescent systems, the design of the systems must be approved for safety. Such approval can be time consuming and costly.
Due to the size of the ballasts and the flourescent tubes, they are not mounted horizontally on the shelves, but rather they are necessarily positioned vertically along the mullion of the doors or frame of erect or free standing refrigeration units. This positioning, as well as the inherent limits of the flourescent tubes light output, creates an uneven lighting across the shelves of the display. For example, the shelving closest to the flourescent tubes has as much as three hundred percent more light than that portion of the shelving in the middle of the door which is between the vertical flourescent tube banks. Due to the size of the flourescent tube banks, the shelving must be a considerable distance from the doors so that the light from the flourescent tube banks is not shielded by posts of the shelving and product closest to the lights.
In open-display refrigeration units, the shelving must necessarily be stepped and staggered with shelves of less width on top and shelves of greater width on the bottom so as not to shield the lower shelving from the flourescent tubes which are positioned along the top of the unit. Usually, only one bank of flourescent tubes is used along the top of the refrigeration unit since placing flourescent tube banks on each shelf would occupy too much shelf space and pose safety concerns.
Another problem associated with the use of flourescent tubes is that the flourescent tubes are produced in pre-set lengths of one foot increments. The designers of refrigeration units must conform their units to these lengths or heights so that the product within the units is adequately lit. This results in ineffective use of the corners and other odd-sized areas of the store, reducing the amount of shelf space available to store and display goods. Shelf space is tantamount not only to the grocery store, but also the suppliers as an increase in only a few inches of shelf space can translate into much more product being displayed and eventually sold. Limiting the shelf space results in lost profits.
Still another problem associated with flourescent tubes is that their thin walls can easily be broken or shattered. The mercury within the flourescent tubes is a health concern. Also, the broken shards of glass is potentially dangerous to consumers within the retail establishment.
In low temperature environments, such as refrigerators and freezers, flourescent bulbs present a particularly costly drawback in that the flourescent bulbs create a tremendous amount of heat. Such heat must be removed from the environment by the compressors, putting strain on the compressors and increasing overall energy costs.
Accordingly, there is a need for an improved lighting system which operates efficiently in low temperature environments such as refrigeration units and the like. What is also needed is a low temperature lighting system which has a longer operational life and reduced maintenance costs in comparison with prior systems. What is further needed is a lighting system which is compact, durable, produces very little heat output, and is not prone to breakage and the emission of noxious gases. Additionally, a low temperature lighting system is needed which occupies less space and more evenly distributes light across the refrigeration unit. Such a system should optimally be flexible in length or height to accommodate the individual needs of the store. Moreover, a low temperature lighting system is needed which is capable of being placed horizontally on a shelf of the refrigeration unit without concern of space constraints or electrocution. The present invention fulfills these needs and provides other related advantages.